In an injection mold of plastic articles, conventional way of making a hole in an injection molded article is effected either by fixing a pin which is configured to have a complementary outer surface to the hole inner surface to be made in a mold cavity prior injection mold, or by subsequent boring step after the article is taken out of the mold.
However, in the above-described method of fixing a pin in a mold cavity, molten plastic material in the cavity flows around the pin and join together forming a linear mark or weld mark. Up to the present, it was impossible to eliminate this weld mark entirely. Further, the weld mark is not only of bad appearance, but also defective in having low strength and requires a reinforcemental thickening of the molded article.
Also, the above-described latter method of subsequent boring is effected to avoid such a weld mark. This subsequent boring of the hole is made after the mold is cooled and the article is taken out of the mold. Although this method is very commonly used as a sure method of eliminating the weld mark, it is not ideal method since it requires additional steps after injection mold, and furthermore, effects a high production cost and increase in a faulty article having cuts or cracks etc.